Tiburon hopes reward cracks homicide mystery

A year has passed since a 75-year-old woman was shot just steps outside her Tiburon home, but police still do not know who committed the affluent city's fourth homicide in 40 years - or why.

Trying to jump-start the investigation into the killing of Joan Rosenthal, authorities announced a $25,000 reward Tuesday for information leading to a conviction. A Tiburon attorney forwarded the money from a donor who wished to remain anonymous.

Rosenthal was, in the words of city Police Chief Michael Cronin, "one of the most unlikely of victims."

A former career counselor at College of Marin, she was found by a friend at her home at 647 Hilary Drive at about 9:40 a.m. on Sept. 22, 2009. She was lying in an enclosed patio near the entrance to her home.

There were no signs of robbery, police said. Rosenthal had lived alone since her husband of 48 years, attorney Kenneth Rosenthal, died earlier in the year.

"Frankly, we don't know," Cronin said, referring to a motive.

"Murders where we clearly have a motive - passion, greed, or something like that - are usually solved very quickly," the chief said. "In murders where a motive isn't clear, you drop into a 25 to 30 percent solve rate."

Cronin said the Marin County Sheriff's Department, which is leading the probe, has spent nearly 4,000 hours on the case, interviewed more than 100 people, traveled as far as New York and Central America, and used FBI profilers and polygraph tests.

Tiburon investigated just five violent crimes all of last year. The city had one homicide, four assaults, no robberies and no rapes.